1. Field of the Invention
The present invention relates to the field of inductive devices, and more particularly to wire core inductive devices such as transformers, chokes, coils, ballasts, and the like.
2. Description of Related Art
It is common for low frequency application transformers and other inductive devices to be made up on a magnetic core comprising a plurality of sheets of steel, the sheets being die cut and stacked to create a desired thickness of the core. For many years the thickness (thus number of necessary pieces) of the stampings has been determined by a strict set of constraints, e.g. magnitude of eddy currents versus number of necessary pieces. The individual sheets of selected thickness are generally oxide-coated, varnished or otherwise electrically insulated from one another in order to reduce/minimize eddy currents in the magnetic core.
The present inventor has developed wire core inductive devices such as transformers, chokes, coils, ballasts, and the like having a magnetic core including a portion of a plurality of wires rather than the conventional sheets of steel. The end portions of the plurality of wires extend around the electrical windings and are arranged to substantially complete a magnetic circuit or flux path. These devices and related methods of manufacturing these devices are set forth in detail in U.S. Pat. Nos. 6,239,681 and 6,268,786, which are incorporated herein by reference.
One particular aspect of these wire core devices is the use of a band or the like to secure the end portions of the plurality of wires in an overlapping or an end-to-end substantially abutting arrangement. Although these arrangements are sufficient to complete a magnetic circuit or flux path, the reluctance of the path is highly dependent upon an effective gap that may exist between the end portions of the wires. The effective gap is generally considered to be an air gap in most applications. The effective gap present in the wire core inductive devices of the above-identified patents, as well as in conventional inductive devices, serves the useful purpose of reducing the negative effects of in-rush currents. It is desirous to be able to control the effective gap so as to provide suitable gap dimensions in a wide range of applications such that the gap can range from an appreciable and dominating factor in the magnetic circuit to an essentially zero gap condition.